This invention relates to novel, synthesized, biologically active sugar esters, a method for making them, and to their use as effective, environmentally safe pesticides. In addition, a pesticide composition and a method of using the composition are disclosed. The novel compounds are capable of controlling arthropod plant pests such as greenhouse whiteflies, sweetpotato whiteflies, aphids and mites. The compounds can be applied as a dispersion in water.
Arthropod plant pests cause extensive and severe damage to major agricultural commodities, both in the field and in the greenhouse environment. In addition to feeding damage, many of these insects also transmit viral diseases. Insects such as whiteflies and aphids deposit their excrement or xe2x80x9choneydewxe2x80x9d on leaves, thus providing a favorable environment for the production of fungi such as sooty mold, which reduces photosynthetic activity and crop quality.
Infestations by the new B strain of the sweetpotato whitefly have proven particularly devastating to growers from Florida to California and as far north as New York and Ohio. The insect has a wide host range, which includes over 500 species of plants. Two dissimilar species, the greenhouse whitefly and sweetpotato whitefly, alone have caused economically significant damage to poinsettia, hibiscus, tomato, crossandra and other plants in a greenhouse environment. The greenhouse whitefly, native to North America, is now world wide in distribution and is resistant to most synthetic pesticides. The sweetpotato whitefly, not limited to the greenhouse environment, is particularly difficult to control on low crops, because it develops on the lower leaf surface that is difficult to adequately cover with pesticides. It also has the ability to change host plant and to acquire resistance to chemical pesticides. The recent rapid spread of strain B of this whitefly has caused significant economic losses to growers of cotton, melons, squash, sugar beets, lettuce, carrots, tomatoes, peanuts, alfalfa, and ornamental plants. In addition, it is a vector for more than 70 diseases including 25 viruses. Following serious whitefly infestations, several agricultural regions have been subjected to viral diseases such as pepper necrosis and yellowing of lettuce.
Whiteflies are generally tropical in distribution, however the sweetpotato whitefly is now believed to have spread in the United States with impunity because of a high level of insecticide resistance and insignificant natural enemies. There have been some efforts to establish populations of parasitoids, which apparently reduce or suppress the insect in its native habitat.
Currently, there are very few commercial pesticides that completely control whiteflies. The insect has a complex life cycle where the egg and pupal stages are generally resistant to chemicals. The entire life cycle is very short (approximately one month), resulting in a rapid increase in population. A severe infestation often occurs before a grower recognizes the problem, making eradication even more difficult. The infestations are rarely localized since the adult can readily take flight and the immature stages are distributed on bedding and ornamental plants. It can also develop a resistance to chemical insecticides fairly quickly, requiring control methods utilizing an alternative schedule of chemicals.
In choosing an effective pesticide, the mode of action is an important factor. The whitefly uses a piercing and sucking system to extract food from the phloem of the infested plant and its stylets can penetrate through a dry film of pesticide on plant tissue, without serious consequence from the pesticide. Therefore, control approaches are limited to either a systemic pesticide which penetrates the leaf surface or is absorbed by the roots and is ingested by the insect or a contact pesticide which penetrates or acts directly on the insect.
Long chain fatty acids (particularly C12) and fatty acid soaps have been reported as effective in the control of insects (Kabara, ACS Symposium Series, No. 325, 1987). In addition, various species of Nicotiana plants have been shown to have resistance to infestation by green peach aphids (Thurston et al., Ent. Exp. and Appl., 1962 and Burk et al., J. of Econ. Ent., 1969), two-spotted spider mites (Patterson et al., J. of Econ. Ent., 1974), tobacco hornworm (Jones et al., Entomol. Exp. Appl. 1985) and greenhouse whitefly (Neal et al., Tob. Int., 1987). Recently, Goffreda et al., (J. Amer. Soc. Hort. Sci 115(1):161-165, 1990) indicated that epicuticular glucose esters were associated with aphid resistance in hybrids with wild tomato. Severson, et al., (Natural and Engineered Pest Management Agents, ACS Symposium series #551, 1994) showed that topical applications of sucrose esters to apterous aphids were toxic. Also, Buta et al., (Phytochemistry 32(4):859xe2x80x94864, 1993) have shown sucrose esters from Nicotiana gossei are potent pesticides against the greenhouse whitefly. As more and more studies are showing the potency of naturally-occurring sugar esters as pesticides, the need exists for the identification and development of specific synthetic sugar ester pesticides against soft-bodied arthropod insects. The advantage of sucrose esters is their superior control and their natural compositionxe2x80x94fatty acids and sugar. Conventional pesticides are usually chlorinated or nitrated aromatics. The extraction of sucrose esters from plants of various species of Nicotiana is possible, although a labor intensive process. Various Nicotiana species have been grown and their cuticular sucrose esters extracted and characterized in a study of ovipositional behavior of the tobacco budworm (Severson, et al., Naturally Occurring Pest Bioregulators, ACS Symposium Series #449, 1991). It was found that sugar esters occurred in amounts of traces to 526 xcexcg/cm2 of leaf surface depending on the Nicotiana species. The most potent sugar esters came from plants such as Nicotiana gossei, which will yield at most about 120 mg/plant. Thus, natural plants will not likely become economical sources of millions of kilograms/year of sugar esters needed to control whiteflies or aphids in this country. Therefore, there is a need for a synthetic method for producing specific, biologically-active sugar esters which have the capacity of controlling whiteflies and other soft-bodied arthropod pests.
There are several methods for producing sugar esters on an industrial scale, as developed by the food industry in the early 1960""s. High molecular weight fatty acid sugar esters, such as sucrose esters of palmitic, stearic, and oleic acids, are used in a wide variety of food products such as baked goods, beverages, spices, soups; in cosmetics such as soaps, lotions, creams; as emulsifying agents; bodying and bulking agents; and for encapsulating pharmaceuticals and other products. One method is a solvent process which produces sugar esters by reacting fatty acid methyl esters (FAME) with sucrose in solvents such as dimethylformamide or dimethylsulfoxide, in the presence of a basic transesterification catalyst and at a high temperature (Weiss, et al., J. Am. Oil Chem. Soc. 49:524, 1972). Sucrose polyesters can also be prepared by interesterification between molten sucrose and FAME of long chain fatty acids at 170xc2x0-187xc2x0 C., catalyzed by lithium, sodium and potassium soaps in the absence of solvents (Feuge et al., J. Am. Oil Chem. Soc. 47:56, 1970). A less drastic process (e.g., U. S. Pat. No. 4,683,299) utilizes fatty acyl chlorides as acyl donors in anhydrous solvents. However, although the patent discloses that the reaction can be achieved at room temperature to 250xc2x0 C., it is stated that the reaction should be initiated by adding the organic acid chloride slowly to the sugar-solvent mixture at relatively low temperatures of about 90xc2x0 C. to about 116xc2x0 C. At this temperature, the reaction is complete after 35 minutes. For temperatures from about 30xc2x0 C. to 55xc2x0 C., the time may range from 24 to 60 hours.
The principal objects of the present invention are to provide a novel method for synthesizing sugar esters of low molecular weight acids which does not require high reaction temperatures or an aqueous purification method and to demonstrate their biological activity.
It is therefore an object of the present invention to provide a method for synthesizing large quantities of sugar esters.
Another object of the present invention is to provide a method for synthesizing, at low temperatures, large quantities of low molecular weight aliphatic acid sugar esters.
A further object of the present invention is to provide a method for separating sugar esters into specific groups using anhydrous purification steps.
Another object of the invention is to provide novel, specific chemically synthesized sucrose esters having acyl substituents on both the fructose and glucose moieties.
A further object of the invention is to provide a pesticide composition comprising novel chemically synthesized sugar esters in a pesticidally effective amount.
A still further object of the present invention is to provide a method of treating soft-bodied arthropod plant pests by administering effective amounts of a pesticide composition containing sugar esters to areas suspected of infestation.
Further objects and advantages of the invention will become apparent from the following description.